The function regulator appliance according to Fränkel (FR I to FR IV)

These bimaxillar appliances have to be seen as functional orthopedic exercise devices with labial and buccal shields

General prerequisites for the FR I - IVThe buccal vestibule has to be measured intraorally in order to be able to carve the upper model for the labial pads and vestibular shields. Normally the orthodontist should carve the model himself during the appointment. If not, he has to give the technician exact measurements which have to be transported onto the model.

The thickness of the wax relief is measured with a probing instrument, and should be 3 mm in the area of the teeth and 2.5 mm in the vestibular sulcus. The wax relief has to be done with the greatest care because only then a correct adjustment of the appliance and an expansion of the dentoalveolar ridge are guaranteed.

Function: FR IThe function regulator type I is planed for the transversal and sagittal compression of an Angle class I and II and for a slight developmental inhibition of the apical base. It is also used in the class II-1 without an increased overbite and without a notorious mesial migration of the lateral segments. Components: 2 vestibular shields, 2 lower labial pads, 1 lingual shield with lingual bow, 1 palatal wire with occlusal rests, 2 canine loops in the upper jaw and the support or connecting wires of the pads and shields.

In the FR I the wire diameter for the labial bow in the upper jaw is 0.9 mm. The canine loop (wire diameter 0.9 mm) starts in the distobuccal aspect of the canine, it is bent completely around the canine and ends buccally in the lateral shield between the canine and the first premolar. The palatal wire with rest is bent out of 1.0 mm wire

In the lower jaw, the support wires between the labial pads and the vestibular shields as well as the connecting wire for the pads are 0.9 mm strong.

The connecting wire between the vestibular shield and the lingual shield is bent out of 1.0 mm wire. The lingual bows and the stiffening wire are bent out of 0.8 mm wire in this example.

The lingual shield of the FR I is designed in such a way that the lingual bows lie free and only the stiffening bow and the connecting wires are grasped with an acrylic pad.

The acrylic shields and the pads have a thickness of approximately 2.0 mm. The length of the vestibular shields has to correspond to the extension of the carvings.

Function: FR IIThe function regulator type FR II has its application in the class I with retrusion of the incisors and increased overbite, in the class II-1 with extreme protrusion of the upper incisors and increased overbite as in the class II-2.Components:The FR II consists of 2 vestibular shields and 2 lower labial pads, the lingual shield and the palatal wire. It differs from the FR I only in the modified canine extensions in the upper jaw and the protrusion bow.

For the protrusion bow or upper lingual wire the model has to be carved deeply between the canine and the first premolar. The other elements are bent according to the FR I.

Only the canine extension is bent in a different way as in the FR I. It runs along with a parallel bent wire over the labial surface of the canine and then is bent upwards to finish with its retention in the vestibular shields.

To activate the anterior segment of the vestibular shield and the connected lingual shield, the vestibular shield has to be sawed open and the vertical sawing line widened with a wax knife.

The lingual shield and the protrusion bow should not hinder each other.

For the FR III the wax relief on the model has a different shape. The model has to be carved more than usual in the area of the upper lip pads. The wax relief is only added onto the upper model as in the area of the upper lip pads. Additionally, with a thin drill, a groove is grinded into the lower front in height of the gingival papilla in order to guarantee a tight fit of the lower labial bow onto the teeth.

The wire elements for the FR III: lower labial bow, 2 occlusal rests on the last lower molars, 1 protrusion bow or upper lingual wire in the upper jaw as well as the support wires for the lip pads and vestibular shields. If necessary, occlusal rests can also be added in the upper jaw.

In the mandible, the vestibular shields fit closely opposite to the upper jaw. When all the wire elements are bent, acrylic is added and the appliance is finished.

Function: FR IVThe function regulator type IV is used in class I patients with skeletal open bite, especially as early treatment in the first mixed dentition. Another application area is the bialveolar protrusion in the mixed dentition. In these patients a labial bow is added in the mandible.Components:2 lower labial pads, 2 vestibular shields, protrusion bow, occlusal rests and palatal wire.

The wax layer of the FR IV is designed as in the FR I and FR II. The occlusal rests can be designed individually respecting their form and location; they should avoid interfering with the distal traslation of the FR IV. Interdental erasements and rests of the lateral shields have to be avoided.

The elements in the upper jaw are: 1 labial bow, 2 occlusal rests led on the first molars from distal, 2 occlusal rests on the first premolars and 1 palatal bow that runs behind the first molar. In the lower jaw, the connecting wires and the rests on the first molars are bent.

In the FR IV the occlusal rests and the labial pads contact the model in contrast to both lateral shields.

Function regulator with integrated screw In all Fränkel appliances the vestibular shields can be replenished with screws. This allows a posterior activation of the lip pads if necessary. The wire elements are bent following the planned design and the screw is fixed onto the wax relief.

Acrylic is added on the function regulator, in this case, a FR II; it is finished exactly as usual and then the sawing cut is realized.

When the pads shall shield the lip further off, both screws are activated parallel.